The present invention relates to a reflection-type liquid crystal display device and a process for producing the same. The reflection-type, liquid crystal display device comprises no light-emitting source by itself and thus its power consumption is lower and its shape can be made more compact than those of a backlight-type, liquid crystal device having a light source.
The reflection-type liquid crystal display device can be further classified into two types, i.e. type of an external light reflector provided outside the liquid crystal cell and type of internal light reflector layer provided inside the liquid crystal cell by vapor-deposition of such a metal as aluminum, silver, etc.
The reflection-type liquid crystal display device of internal light reflector type has a narrower gap between the display surface and the light reflector layer surface than that of the external light reflector type, and thus is free from shadow generation in the dark display region, which has been a problem in the external light reflector type, and also a high possibility of higher resolution can be expected. In case of an internal light reflector-type, color liquid crystal display device using a color filter, the displayed color can have a high color purity. Particularly incase the light reflector layer is electroconductive, the light reflector layer can be used as an electrode for applying a voltage to the liquid crystal layer at the same time.
In case of the reflection-type, liquid crystal display device, it is also necessary to scatter the reflected light. In this connection, JP-A-8-201802 and JP-A-9-113893 disclose a technique of providing the display device with a light-scatterable medium. JP-A-6-167708 proposes a method of forming a light-scattering surface on a light reflector layer acting also as an electrode by forming an uneven surface on the light reflector layer to give asperity thereto.
In case of the internal light reflector-type, liquid crystal display device, a light reflector layer is formed by vacuum vapor deposition of a metal, resulting in complication of process steps for producing a liquid crystal display device and also increase in the product cost. When the light reflector layer is used also as an electrode at the same time, a step of forming an electrode pattern, for example, patterning of a metal by photolithographic process, becomes a cost increase factor.
An object of the present invention is to provide a reflection-type liquid crystal display device having an internal light reflector layer, which can be produced in simple processes, and a process for producing the same.
In the present reflection-type liquid crystal display device, pattern formation of the light reflector layer can be made with ease and improved display quality.
A reflection-type liquid crystal display device according to the present invention comprises a pair of substrates, at least one of which is transparent, a liquid crystal layer sandwiched between the pair of substrates, and a light reflector section provided between the liquid crystal layer and one of the pair of the substrates, the light reflector section including a polymeric medium layer with fine silver particles precipitated on the surface. The fine silver particles reflect light.
A process for producing a reflection-type, liquid crystal display device according to the present invention comprises applying a mixture comprising monovalent silver and a photo-sensitive polymeric medium to a substrate, exposing the applied mixture to light, thereby photolithographically forming a light reflector layer of desired pattern, heating the light reflector layer under a predetermined temperature condition, thereby precipitating fine silver particles on the surface of the light reflector layer, and confronting a transparent substrate different from the light reflector layer-formed substrate with the light reflector layer-formed substrate to sandwich the liquid crystal layer the two substrates.
Another process for producing a reflection-type liquid crystal display device according to the present invention comprises the following steps, i.e. forming an electrode for actuating liquid crystals on a substrate, forming an insulating layer on the electrode, applying a mixture comprising monovalent silver and a photosensitive polymeric medium to the insulating layer, exposing the mixture to light, thereby photolithographically forming a light reflector layer of desired pattern, heating the light reflector layer under a predetermined temperature condition, thereby precipitating fine silver particles on the surface of the light reflector layer, confronting a transparent substrate different from the light reflector layer-formed substrate with the light reflector layer-formed substrate to sandwich the liquid crystal layer between the two substrates.
According to one embodiment of the present invention, the surface of the light reflector layer can be made electroconductive or non-conductive by adjusting the amount of silver to be contained in the polymeric medium. The surface of the electroconductive light reflector can act also as an electrode for actuating liquid crystals. The surface of the non-conductive light reflector layer can act also as an orientation layer.
According to another embodiment of the present invention, use of a silver-containing photosensitive polymeric medium as light reflector layer materials ensures easy photolithographic patterning of the light reflector layer.
According to other embodiment of the present invention, it is preferable to provide a scattering layer for scattering the reflected light. In place of providing a scattering layer, addition of an appropriate amount of fine non-conductive particles to the polymeric medium can give unevenness to the surface of the light reflector layer by the presence of the fine non-conductive particles therein, thereby enhancing a light scatterbility.